24 Cardiovascular Reflexes and Regulation of Blood P & V Flashcards
What is the primary mechanism for short term regulation of BP?
baroreceptor reflex in carotid sinuses and aortic arch
What are sensory nerve endings that detect and signal the CNS of changes in BP?
baroreceptors
What are the 2 main outcomes of baroreceptor activity?
- inhibit efferent sympathetc
2. activates parasympathetic pathway.
What is the major function of the baroreflex?
buffer or oppose changes in BP
What nerve innervates the carotid baroreceptors?
CNIX
What nerve innervates the aortic baroreceptors?
CNX
Afferent fibers of the baroreflex synapse where?
medulla oblongata–nucleus tractus solitarius
Do baroreceptors fire more often in an expanded artery(i.e. High BP) or in a smaller artery (i.e.. low BP)?
Higher BP and stretch leads to malformation and increased firing of the AP to the brain.
What are the 3 main determinants of baroreceptor activity?
- Mean arterial BP
- Rate of change in pressure
- Large artery compliance
What is the minimum pressure baroreceptors fire AP?
Pressure threshold- 40-60 mmHg
Pressure above which the arterial baroreceptors no longer increase their firing?
Saturation Pressure – 180mmHg
What are the main responses to increase of baroreceptor activity?
decrease SNA, increase paraSNA, and decrease AVP
What are the main responses in a decrease of baroreceptor activity?
increase SNA, decrease paraSNA, increase AVP
Does baroreceptor activity adapt to sustained increase?
yes an it does not take very long…10 minutes and leads to rapid resetting or (right shift) of pressure activity curve. [decrease is the opposite]
what happens to baroreceptor sensitivity in chronic hypertension?
it decreases—leads to increased BP variability, arrhythmias, sudden cardiac death, promotes high SNA/ low paraSNA
What type of nerve endings are found in the heart?
mechanosensitive (central blood volume) and chemosensitive (myocardial ischemia)
What nerve is very important for normal reflex control of circulation?
vagus afferents
When are SNA afferent fibers activated in the heart?
disease states (along with vagal afferents)
Increased cardiac vagal afferent activity triggers what 2 responses?
decrease SNA, decrease AVP—–lower BP
What reflex response would occur in mild-moderate hemorrhage or orthostatic stress?
increase SNA, vasoconstriction, and increase HR
What reflex would you expect in severe hemorrhage or prolonged orthostatic stress?
increase paraSna, decrease HR, decrease SNA, decrease TPVR—-hypotension
What results from paradoxical activation of vagal afferents innervating left ventricle stimulated by vigorous pumping of underfilled ventricles or chemicals released by myocardium?
vasovagal syncope (neurocardiogenic syncope)
Can the CNS trigger syncope?
yes- perturbed cerebral blood flow or emotional stimuli (less understood)
Hypoxia, apnea, hypovenitilation, respiratory disease and metabolic disorders cause abnormalities of arterial blood gases and pH. Where are these changes sensed in the blood?
carotid and aortic bodies
